1. Field of the Invention
The present invention relates to a vehicle anti-theft engine control device and, more particularly, to a vehicle anti-theft engine control device which can be mounted on both a vehicle which is equipped with an anti-theft function, and a vehicle which is not equipped with the anti-theft function.
2. Description of the Related Art
Among the preventive measures which have been proposed, there is one in which a vehicle is immobilized by a mechanical and/or electrical means if someone attempts to start or drive the vehicle by using an illegitimate key. For this purpose, the key incorporates a memory for an identification code (hereinafter referred to as "ID code"), so that, whenever the key is inserted in a key cylinder to start the vehicle, the key ID code is read and referred to a reference ID code which has been stored in the vehicle beforehand. Only when the read ID code matches the reference ID code, an enable signal is issued and only when an engine control unit or circuit legitimately receives the enable signal, the engine is allowed to be started. In this case, there is an apprehension of the theft being committed by mechanical damage or illegitimate wiring if a binary signal (simple ON/OFF signal) is used as the enable signal. To eliminate such an apprehension, it has been proposed to code the enable signal (refer, for example, to pages 59 to 64 of No. 8, vol. 48, 1994 "Automotive Engineering").
One of such conventional transponder type immobilisers is shown in FIG. 4. A key 2 incorporates a memory (not shown) which has a key ID code (e.g. 64-bit code) stored in advance, and a transmitter 4 for transmitting the key ID code. The transmitter 4 of the key 2 and a key cylinder 5 are coupled with an inductive coil (antenna) 6, for example. When the key 2 is inserted and turned to the ignition position on, an ignition switch 7 is closed. This activates an immobilizer CPU 13 to cause a power amplifier 11 of an immobilizer ECU 10 to supply electric power to the transmitter 4 via the coil 6. The transmitter 4 then reads the key ID code and sends it to the key cylinder 5 side.
The received ID code is detected and digitized by an R/F (high-frequency) circuit 12 in the immobiliser 10, and it is read into the CPU 13 where it is temporarily stored in an appropriate ID code register 13B. An unique reference ID code assigned to each vehicle is stored beforehand in an EEPROM 13A of the CPU 13, this reference ID code is compared with the key ID code which has been read, by a code checking unit 13S of the CPU 13. When the two ID codes match or when they are found to have a predetermined relationship, the enable code is sent from the checking unit 13S to an engine ECU 16. At the same time, a starter relay is energized to rotate a starter motor (not shown).
When the engine ECU 16 has determined and verified the received enable code, the engine ECU 16 controls a fuel injection valve 17, a fuel pump 18, an ignition control unit 20, etc. according to a predetermined procedure and timing to enable the start and travel of the vehicle. If, however, the read key ID code, which has been transmitted from the key 2, does not match the reference ID code stored in the EEPROM 13A or does not have the predetermined relationship thereto, then the checking unit 13S does not send out the enable code. Thus, the start of the vehicle by the engine ECU 16 is prohibited and also the CPU 13 energizes an alarm 14 to give an appropriate alarm or display. In this way, the illegitimate start and running of the engine by the illegitimate key is prevented, thus ensuring the protection of the vehicle against theft.
Japanese Utility Model Publication No. 63-50204 has disclosed a proposal to integrate this type of vehicle anti-theft function or the code checking function into an IC circuit board of a conventional engine control unit which is not equipped with the vehicle anti-theft function.
The transponder type immobilizer described above provides an excellent advantage for preventing the illegitimate engine start and running and for preventing the vehicle theft. In addition, integrating the vehicle anti-theft function and the code checking function into the conventional engine control unit provides an advantage of the need for fewer parts and fewer assembly man-hours. On the other hand, however, there are various kinds of specifications for the vehicle anti-theft function, including the U.S. specifications, EC specifications, and immobilizer specifications. This requires many different types of engine control IC circuit boards for the different kinds of specifications, presenting a problem in that troublesome management is involved and higher development and manufacturing cost is unavoidable.